mm/page_io: use a folio in swap_writepage_bdev_async()

Saves one implicit call to compound_head().

Link: https://lkml.kernel.org/r/20230721034451.16412-9-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_io.c

@@ -352,6 +352,7 @@ static void swap_writepage_bdev_async(struct page *page,
 		struct writeback_control *wbc, struct swap_info_struct *sis)
 {
 	struct bio *bio;
+	struct folio *folio = page_folio(page);
 
 	bio = bio_alloc(sis->bdev, 1,
 			REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc),
@@ -362,8 +363,8 @@ static void swap_writepage_bdev_async(struct page *page,
 
 	bio_associate_blkg_from_page(bio, page);
 	count_swpout_vm_event(page);
-	set_page_writeback(page);
-	unlock_page(page);
+	folio_start_writeback(folio);
+	folio_unlock(folio);
 	submit_bio(bio);
 }